In an office environment, desk top telephone service, voice mail service, and fax service is typically provided by a private telephone communication system. Private telephone systems comprises key switch systems, private exchange (PBX) systems, and more recently, voice-over-internet-protocol (VOIP) systems.
A key switch system consists of central key switch unit and a plurality of desk top telephones and fax machines. Each telephone is coupled to the key switch unit by a subscriber loop running from the telephone to the key switch unit. Communication between each desk top telephone and the key switch unit typically utilizes plain old telephone service (POTS) signaling.
The key switch unit may be coupled to a voice mail server by a proprietary interface. The key switch unit is further coupled to the public switched telephone network (PSTN) using trunk lines that are connected to a central office switch that is typically managed by the local telephone service provider.
Each telephone includes a plurality of buttons (and illuminated indicators), each being associated with one extension or one of the trunk lines to the central office. When an extension or a trunk line is in use, the indicator associated with that extension will be illuminated on all of the other telephones such that the operators can view which extensions and trunks are in use, and which are available. When an operator desires to telephone another extension, he or she will activate the button associated with the other extension. When an operator desires to telephone a subscriber loop of the PSTN, the operator first activates a button associated with an outside line (which will cause the key switch unit to couple an outside line to the operator's extension giving the operator's extension a PSTN dial tone) and then dial the number.
A PBX system comprises a switching network, a plurality of desk top telephones, and a voice mail server. The voice mail server is typically coupled to the switching network using a proprietary interface. Each desk top telephone and fax machine is coupled to the switching network by an extension line that consists of twisted pair conductors that are terminated by a telephone jack in the office. Communication between the desk top telephone and the switching network over each extension line utilizes either proprietary digital signaling or plain old telephone service (POTS) signaling. The switching network is further coupled to the public switched telephone network (PSTN) using trunk lines that are connected to a central office switch that is typically managed by the local telephone service provider. The switching network controls calls between extensions and between an extension and a remote destination via a trunk line coupled to the PSTN.
PBX systems do not typically have a button associated with each extension on each telephone. Instead, operators dial each other's extension numbers for placing internal calls and typically dial “9” to get an outside line for placing calls over the PSTN.
VOIP systems utilize a central gateway and a plurality of VOIP telephone stations. Each station is coupled to a packet switched network (such as an Ethernet network) that interconnects each station with the central gateway. The central gateway and each telephone station typically is assigned an IP address and communications between two extensions and between an extension and the gateway typically is over UDP/IP channels. Because of the wide spread acceptance of PBX systems, VOIP systems typically are configured such that operators dial each other's extension numbers for placing internal calls and typically dial “9” to indicate a call to be placed over the PSTN.
It is generally recognized the dialing of extension numbers and dialing “9” for an outside line has several advantages over key systems, particularly in larger environment where there are many extensions. However, in a small office environment, key switch systems have some advantages over PBX systems.
First, each operator can quickly determine whether another operator is on the telephone without having to first attempt to place a call and receive a busy signal (or roll to voice mail) if the operator is on the telephone. Secondly, each operator can quickly determine whether an outside line is available without having to first try to place a call and receive a busy signal if an outside line is not available. Thirdly, an incoming call on one of the trunk lines can typically be answered by any extension simply by activating the button associated with the ringing trunk line.
What is needed is a communication management system that provides a typical key switch user experience while providing the flexibility of VOIP networking.